This invention relates to a light pen input system comprising a light pen which emits a light beam and a light sensing device comprising a planar array of light sensing elements in rows and columns over which the light pen is moved, the light beam emitted from the light pen producing a light spot on the array which is sensed by the sensing elements.
Examples of such systems are described in EP-A-0 491 436, EP-A-0 587 236 and EP-A-0 572 182, in which the light sensing element array is integrated with a liquid crystal display element array to provide a combined display output and light sensing input system. In EP-A-0 491 436 and EP-A-0 487 236 the light sensing element array consists of a two-dimensional, planar, row and column matrix of photoelectric elements, such as photodiodes, photoresistors, or the like, which are addressed via sets of row and column address conductors. Light emitted from a light pen and falling on sensing elements in the array produces electrical responses which are detected by a detector circuit connected to the sets of row and column address conductors that provides an output indicative of the elements illuminated. In EP-A-0 572 182 two sets of optical light guides are provided extending in X and Y directions respectively, which define at their intersections a two-dimensional, X-Y, matrix of sensing elements. The sets of light guides are connected at their ends to respective photosensing circuits which produce an electrical signal in response to light being conducted thereto by the light guides. Light from a light pen falling on the area of an intersection between a light guide of each set produces outputs from the photosensing circuits which uniquely identify the area concerned.
Similar kinds of light sensing devices without a combined display element array can be used as a pen input device to a personal computer or other data processing equipment having a separate display.
The combination of a light pen and light sensing device can be used, for example as a graphics tablet type input device for a computer system, in a manner similar to that provided by alternative kinds of input devices which utilise resistive, acoustic, induction or electrostatic sensing techniques, in which the X-Y position of the pen as it moves over the array is sensed and an output provided accordingly to the computer system. The combined light display/sensing devices can be used in equipment such as notebook computers, PDAs, electronic message pads, notebooks, organisers and the like to enable information to be displayed and inputted using a light pen whereby, for example, as the light pen is moved over the surface of the light sensing array not only is the X-Y movement of the pen sensed but also the signals obtained indicative of the pen position are used to produce a display output from the display element array in accordance with such movement to give the impression of writing on paper.
It should be understood that the term light used herein is intended to include both visible and non-visible, e.g infra-red, electromagnetic radiation.
Light pens commonly used in such systems comprises a source of light, for example an LED or semiconductor laser, a power supply and a lens arrangement which concentrates the light and directs an output beam through the tip of the pen. The light beam is such that, with the pen held perpendicularly to the plane of the sensing element array, the light spot produced is substantially circular. An example of light pen is described in EP-A-0 572 182 in which the pen's output is pressure responsive with the diameter of a light spot produced by the pen on a writing surface of the light sensing device is increased as the pen is pressed harder against the surface so that, in effect, thick and thin lines can be drawn by the user varying the pressure of the pen on the surface to control the diameter of the light spot incident on the sensing element array, and thus the number of sensing elements upon which the beam is incident at any given time.